This invention concerns the handling of calls that are forwarded to a mobile telephone.
Call transfer is one of the most commonly used services in modern telecommunication networks. In the service a subscriber can specify that calls destined to him are to be forwarded to another subscriber""s number. For example, Beth can transfer her calls to Cindy when leaving her home to visit Cindy. A subscriber can specify that his calls be forwarded in various situations. For example, when the CFU (Call Forwarding Unconditional) service is activated, all the calls destined to the subscriber are forwarded to a given number. In the CFB (Call Forwarding on Busy) service, calls are forwarded if the called subscriber is busy. By activating the CFNRy (Call Forwarding on No Reply) service, the subscriber instructs that his calls are to be forwarded after 4 alert tones, for example, if the call is not answered before that. For mobile subscribers the CFNRc (Call Forwarding on Not Reachable) service can be defined. In CFNRc the calls are forwarded if the subscriber is not in the coverage area of the mobile telecommunication network, or if he has turned his mobile station off.
The routing of forwarded calls, as well as the charging principle for forwarded calls, are shown in FIG. 1. In the figure, the calling party A makes a call to B. B has forwarded his calls to C. This is done by giving the exchange of B instructions to forward the calls addressed to B to a third party C. Both B and C are fixed network subscribers. A may be a fixed network subscriber or a mobile network subscriber. The call is first routed from A via his Local Exchange LE(A) to the local exchange LE(B) of B. Information concerning the specified call forwarding is stored in LE(B). In response to having received the request for call establishment from LE(A), LE(B) notices that the call is to be forwarded to C. In response to that, LE(B) routes the call to the forwarded to party C via the local exchange LE(C) of C. LE(B) becomes the transit point of the call. The first call leg from A to LE(B) is paid by subscriber A. The forwarded leg from LE(B) to C is paid by subscriber B.
In FIG. 2 is shown a situation where the call is forwarded to mobile subscriber. In the example, both A and B subscribers are fixed network subscribers. However, they can also be mobile subscribers without causing any remarkable changes in the process. When compared to the case shown in FIG. 1, the only difference is the leg between LE(B) and subscriber C. This is due to the basic feature of mobile telecommunication systems: the location of the subscriber is not fixed. Therefore, the location of the subscriber has to be ascertained before establishing the connection.
In modern mobile telecommunications networks, the network maintains information about the location of the mobile subscribers. In the GSM network used as an example in this application, this information is distributed between the home location register HLR and visitor location registers VLR directly connected to mobile switching centers MSC. The HLR is in the home network of the mobile subscriber and contains the unchanging subscriber information and the location information of the mobile subscriber with an accuracy of one VLR area. The VLR area typically equals the area served by one mobile switching center. The VLR of the visited mobile switching center VMSC responsible for the area the subscriber is currently visiting contains more exact information about the subscriber""s location.
On the leg from LE(B) to subscriber C, the call is first routed to the Gateway Mobile Switching Center GMSC(C) of subscriber C. GMSC(C) is basically any MSC capable of making interrogations to the home location register HLR(C) of subscriber C. In response to having received the HLR inquiry, i.e. the query for routing information, the HLR ascertains the VLR the subscriber is currently visiting, and sends that VLR, i.e. VLR(C), a request PRN (Provide Roaming Number) for a roaming number.
In response VLR(C) returns HLR(C) a roaming number MSRN (Mobile Subscriber Roaming Number) identifying the called subscriber in this VLR. HLR(C) forwards the roaming number to GMSC(C). GMSC(C) adds to the call record comprising information of the call information that subscriber C is receiving the call in the area on VLR(C). Using the received identification MSRN and the message IAM(MSRN) (IAM=Initial Address Message), GMSC(C) establishes a connection to the MSC VMSC(C) currently visited by subscriber C. To identify the called subscriber corresponding to the received roaming number with his identity number IMSI or TMSI (Temporary Mobile Subscriber Identity) VMSC(C) queries VLR(C), which then returns this information. According to the specifications, this is done using messages SIFIC (Send Info For Incoming Call) and CC (Complete Call). Having ascertained the identity of the called subscriber, VMSC(C) now establishes the final leg of the call to the called subscriber.
In GSM, the basic principle in charging is that the calling subscriber pays the leg between himself and the home network HPLMN(B) (HPLMN=Home Public Land Mobile Network) of the called subscriber. The rest of the route is paid by the called subscriber. The idea here is that the calling subscriber should not have to pay a surprisingly high price for his call, for example, when the called subscriber is roaming in a distant country. According to this principle, when subscriber A in Finland calls a mobile subscriber B whose home network is in New Zealand but who is currently roaming in Finland, the call is routed via New Zealand. Subscriber A pays the leg from Finland to New Zealand and subscriber B the leg from New Zealand back to Finland.
Due to this charging principle, the forwarding subscriber B pays for the leg between LE(B) and the home network of C and subscriber C from his home network onwards. It should be noted that for most operators, reception of calls is free in the home network HPLMN (Home Public Land Mobile Network) of the subscriber. However, when the subscriber is roaming outside his home network, he is charged for the roaming leg from his own home network to the VPLMN (Visited Public Land Mobile Network) he is currently visiting.
The problem with this charging principle is that it is unfair to the mobile subscriber if the call has been forwarded. When the principle is applied, a GSM subscriber who answers a forwarded call is charged for the roaming legs even if he is not the intended recipient of the call. For example, let us consider a situation in which Beth and Cindy travel abroad together. Cindy has a mobile phone, and Beth forwards calls destined to her fixed telephone to Cindy""s mobile phone. Now, when Andy calls Beth, Andy is charged for the local telephone call leg of the call. Beth pays the leg from her own exchange to the HPLMN of Cindy, the price of which is the price of a national call to a mobile telephone. Cindy, in turn, pays for the roaming leg, i.e. from her HPLMN to her VPLMN. In many cases, the roaming leg is the most expensive of all the legs of the call. Thus, even if the call is from Andy to Beth, Cindy is the one who is charged the most.
The objective of this invention is to solve the above-mentioned problem of the prior art. This objective is achieved using the method and apparatus specified in the independent claims.
This invention proposes a new charging principle according to which the roaming leg is paid entirely by the party who forwarded the call to a mobile subscriber.
In an exemplary embodiment, the call is first routed to the exchange of subscriber B, who has forwarded his calls. After determining that the call is to be forwarded to a mobile subscriber C, the exchange routes the call to the gateway mobile switching center GMSC capable of making interrogations to the home location register of subscriber C. The GMSC adds in the call record of the call the information that the call has been forwarded by the called subscriber B.
When generating the charging record for the call, the called subscriber B is charged for the leg between the GMSC and subscriber C. Thus subscriber C does not have to pay for calls addressed to subscriber B. To minimize the call costs to subscriber B, as direct a route as possible is preferably used on the leg between the GMSC and subscriber C. The charging record may be generated in other network elements than the GMSC, such as in the billing center.